1. Field of the Invention
The present invention relates to a process for removing TOC components and an apparatus for removing TOC components which are contained in a liquid, and relates to technology of removing TOC components contained in liquid, such as ultrapure water used in a process for producing a semiconductor, a liquid crystal, or medical supplies.
Priority is claimed on Japanese Patent Application No. 2004-211339, filed Jul. 20, 2004, the content of which is incorporated herein by reference.
2. Description of Related Art
With technological innovation and advance of technology in recent years, in the semiconductor industry, the liquid crystal industry, and the pharmaceutical industry, etc., ultrapure water (pure water) from which TOC components, such as organic matter, pyrogen, and bacteria, not to mention dissolved substances and suspended granular materials, such as ions, are removed as much as possible, is required. Such ultrapure water is produced by an ultrapure water producing system which is constituted by combining a filtrating apparatus, an ion exchanging apparatus, a hyper filtrating membrane apparatus, and a reverse osmosis membrane apparatus, etc., suitably.
However, although this ultrapure water producing system is effective to remove dissolved substances, such as ions and suspended granular materials, etc. contained in the unpurified water which is a processing target, it is not so effective to remove TOC components, such as organic materials, pyrogen, and bacteria, that is, TOC components of 5 to 20 ppb remain in the ultrapure water. If such ultrapure water in which TOC components remain is used in the above fields, there is a possibility that various troubles may occur. For example, when ultrapure water in which TOC components of 5 to 20 ppb remain is used as a rinsing water in producing semiconductors, such as LSIs, these TOC components adhere to the semiconductors as scales to cause contamination of the semiconductor, circuit destruction, etc. thereby lowering the yield of products.
In order to solve the problem mentioned above, for example, patent document 1(Japanese Unexamined Patent Application, First Publication No. 10-151450) discloses a method for reducing TOCs by using a lamp which emits wavelength of 185 nm and 254 nm ultraviolet rays within a pure water tank.
In this method, the oxygen molecules in the tank are changed to ozone by radiating ultraviolet rays with a wavelength of 185 nm within the pure water tank. Furthermore, hydroxyl radicals are generated by radiating ultraviolet rays with a wavelength of 254 nm to the ozone. By the ozone and the hydroxyl radicals which are generated, the TOCs are oxidized and decompose to be eliminated.
Moreover, for example, non-patent document 1 (“Water Handbook” Water Handbook Members-of-Editorial-Board Meeting, Maruzen Co., Ltd., March 31, Heisei 15 issue, p. 316-319, p. 345-347) discloses a method of reducing TOCs using a photocatalyst. In this method, a photocatalyst and an ultraviolet-rays light source are disposed in a pure water tank, whereby ultraviolet rays with a wavelength of 380 nm or less are radiated to the photocatalyst so as to generate hydroxyl radicals on the photocatalyst surface, thereby oxidizing and decomposing the TOCs to be eliminated.
However, in the method of using ultraviolet rays with wavelength of 185 nm and 254 nm, the place in the pure water tank where the ozone and the hydroxyl radicals are generated is not specified, and hence there is a possibility that, when ozone and hydroxyl radicals exist near the rubber packing in the tank, the rubber sealing is oxidized and decomposes to generate cracks, thereby causing a leakage of water.
Moreover, in the method of using the photocatalyst, the photocatalyst is a powder which is made of titanium dioxide as the main ingredient, and hence it is used to be carried on the surface of a base material, etc. Since a photocatalyst is a material which is comparatively hard to use as a coat, a binder is mixed when coating. Such a binder is usually an organic material. Therefore, by receiving ultraviolet rays underwater for a long time, hydrolysis may occur, or the binder itself may be oxidized and the binder may be decomposed by the hydroxyl radicals generated on the photocatalyst surface. TOC of the pure water in a pure water tank may increase by decomposition of the binder. Moreover, the binder decomposes to make the base material unable to hold the photocatalyst, such that the photocatalyst diffuses and flows out to the pure water path, thereby weakening the oxidizing effect and decomposing effect of the photocatalyst.